1. Technical Field
The subject invention(s) are related to arrangements for facilitating the provision and control of additional air, also referred to as scavenging air, to a two-stroke internal combustion engine; more particularly, the invention(s) are directed toward an adaptive thin-body flange, also referred to as a scavenging air transfer member, that is mountable to the engine's carburetor for facilitating the provision of scavenging air to the engine, as well as providing a control valve assembly that regulates the flow of such scavenging air during the engine's operation.
2. State of the Art
Regarding internal combustion engines, and particularly two-stroke engines, increased emphasis is continually being placed on the reduction of fuel consumption and the achievement of cleaner exhaust gases. Two-stroke internal combustion engines have typically been designed with special flow ducts through which fresh air is introduced into the combustion chamber ahead of the air-fuel mixture. In such a scavenging procedure, at the end of the engine power stroke, when the port of the exhaust duct is opened, fresh air is supplied behind the exhaust gases and before the fuel/air mixture. This supply of additional air to the combustion chamber is also called scavenging air. In an ideal state, all of the exhaust gases are pushed out, and this scavenging air acts as a buffer ahead of the air-fuel mixture subsequently coming into the chamber from the engine crankcase. In this buffering capacity, the additional air reaches the exhaust port before it is completely closed by the upward moving piston during the following compression stroke.
What has been described so far are the conditions existing for a two-stroke engine at operational speed. Under these conditions of higher speed engine operation, the percentage amount of additional air is less critical. A problem can arise and become acute, however, when the engine is running at idle speed. In order to keep this idle speed as low as possible, the carburetor is adjusted, typically via adjuster screws, to assure a proper fuel/air mixture for the idling operational speed. This means that the air and fuel must be appropriately metered and allowed to be drawn in by the movement of the piston at proportions that just allow the engine to continue to run smoothly without any risk of stopping unwarrantably. In this low-speed operational range, additional air should not be allowed to enter into the engine, since small variations in the supply of air results in too lean of an air-fuel mixture.
Known valve arrangements for controlling the supply of additional or scavenging air suffer a number of disadvantages. Such valves have typically been of either the barrel or butterfly type, the latter also being oftentimes referred to as a rosette valve. Both types of valves have traditionally been located in the scavenging air duct, and because the inlet to the duct is downstream of the intake muffler, turbulent air flow is experienced in the duct which complicates the control of the proportion of additional air supplied.
When it comes to comparatively small engines for portable working tools, the exactness of such valves is important to achieve sufficiently precise control of the amount of scavenging air. Structurally, these needs for such precision are quite opposite to the design criteria of the balance of such small engines where the demand is for a rugged tool that can be used in a climatologically tough and/or dusty environment. Although the scavenging air traversing such valves has normally been filtered, some smaller particles cannot be separated out and do reach the valves.
Since the valve assemblies of the barrel type have relatively large sealing areas, a small amount of particulate can cause a deficient control function of the valve thus resulting in irregular engine speed and operation. Still further, those abrasive particles that are not filtered out of the scavenging air stream can become stuck to the sealing areas and cause wear to the associated valve components resulting in deterioration of their sealing ability, even after cleaning if damage is done to the exposed surfaces of the components.
In a damp and cold environment, freezing can occur in these valves due to their large sealing areas. The butterfly valve provides widely varying degrees of leakage at closing depending on how rapidly it is being closed. The closing of this type of valve also very much affected by dirt.
Another common reason for air leakage about valve assemblies typically used in such applications is that metal-to-metal contact is usually depended upon for achieving the seal. Because of the hardness of the abutting metal components of conventional valve designs, inexact mating between these components will result in leakage to varying degrees. It has been further recognized as an advantage and purpose of the presently disclosed invention(s) to reduce or alleviate such leakage.
Regarding the ever increasing stringency for improved fuel consumption and emission's quality outlined above with respect to internal combustion engines, as well as the desire to continually increase such engines performance characteristics, designs are frequently changing. These changes can be to the engine itself, and/or the carburetor that is associated therewith. In the case of two-stroke engines, however, the necessity for providing a scavenging air supply does not change. Therefore, there is a constant design criteria for mating such an additional air supply to the engine arrangement, regardless of its design. Heretofore, accommodation of the scavenging air supply has in some instances been incorporated via modification to the carburetor's design; typically at substantial detriment to a new engine's design program with respect to both time delays and increased costs.
The utilization of connective adaptors for facilitating the support of scavenging air assemblies is known. A review of these assemblies, however, reveals certain deficiencies. One example includes the abrupt turning of the flow path of the scavenging air at the adapter. An illustration of such a characteristic may be appreciated from the drawings of JP-9-268917 in which scavenging air enters the adapter (8) flowing generally in a horizontal direction and is abruptly turned ninety degrees to flow further through the scavenging air channel or duct. Necessarily, the scavenging air flow is once again turned ninety degrees at the elbow (6) to flow toward the two-stroke internal combustion engine being supplied the scavenging air. It should be appreciated that each turn in the scavenging air flow path has a resistive effect on the air flow therethrough. Moreover, a series of turns in the flow channel has a cumulative detrimental effect that significantly deteriorates flow efficiency through the channel.
It is for these reasons, as well as others revealed through the study of scavenging air arrangements for two-stroke internal combustion engines, that the present invention(s) have been developed for at least the purposes of providing inexpensive and easy to use scavenging air support adapters whose designs can be readily modified to accommodate different engine configurations, as well as changes in any particular engine design.